Using Goal Directed Techniques for Journey Planning with Multi-criteria Range Queries in Public Transit

Abstract

One of the main problems for a realistic journey planning in public transit is the need to give the user multiple qualitative choices. Usually, public transit journeys involve 4 main criteria: the departure time, the arrival time, the number of transfers and the walking distance. The problem of computing Pareto sets with these criteria is called the Pareto range query problem. This problem is complex and difficult to solve within the constraints of the industrial world of smartphone applications, like a response time of the order of a second. In this paper, we present the Goal Directed Connection Scan Algorithm (GDCSA), an algorithm that allows, for the first time, to solve this problem with run times of less than 0.5 seconds on most European city or country-wide networks, like Berlin or Switzerland. In addition, GDCSA satisfies other industrial needs: it is conceptually simple and easy to implement. It partitions the graph in geographically small areas and precomputes some lower bounds on the duration of a trip in order to select for each itinerary a sub-set of these areas to decrease the number of scanned connections. Combining this sub-set and a journey planning using 4 criteria, the number of scanned connections is lowered by a factor of up to 17 times compared to the best algorithms (CSA and RAPTOR), the number of nodes opened during the search is lowered by a factor of up to 2.9 and the query times are lowered by a factor of up to 9 on metropolitan networks. The integration of GDCSA in a smartphone app backend server led to an improvement in results by a factor of 5.